1. Field of the Invention
The present invention generally relates to a method of and an apparatus for receiving an FM (Frequency Modulation) broadcast electric wave, and more particularly to a method of and an apparatus for receiving RDS (Radio Data System) data, which are transmitted from an RDS broadcast station for transmitting digital data such as character information by multiplexing it to the FM broadcast electric wave, and displaying the received content of the RDS data.
2. Description of the Related Art
There are a plurality of FM broadcast networks in a country since the FM broadcast is more suitable for various geographical conditions than the AM (Amplitude Modulation) broadcast. Thus, there are a very large number of FM broadcast stations on the whole, so that 20 to 50 channels of the FM broadcasts may be received. Accordingly, there is a problem that it is difficult for the user to understand from which broadcasting station the FM broadcast which he is listening to is broadcasted, or what the broadcast frequency of the broadcasting station which he wished to listen to is.
For this reason, there is an RDS broadcast of transmitting data indicating network information, which the broadcasting station belongs to, and character data such as music title information of the broadcasted music and road traffic information by multiplexing those data on the FM broadcast electric wave.
The RDS broadcast is called as an RBDS (Radio Broadcast Data System) broadcast in the United States of America.
In this RDS broadcast, the third higher harmonic wave, which frequency is 57 KHz, of the pilot signal, which frequency is 19 KHz, is used as a sub-carrier wave in a frequency band range outside of that of the FM modulated wave. This sub-carrier wave is amplitude-modulated by data signal, which indicates the information related to the broadcast such as the program content and which is filtered and biphase-coded, to be the RDS data signal. This amplitude modulated sub carrier wave is frequency-modulated on the main carrier to be broadcasted.
The RDS data signal has a base band coding structure as follows.
Namely, the RDS data signal has a plurality of blocks each consisting of a plurality of bits. The groups are repeatedly multiplexed to be broadcasted. Each block consists of an information word and a bit check word. Some of the blocks have an RT (Radio Text) data, which are the character data.
Here, in this type of RDS receiving system, the character sequence is transmitted which has one meaning by use of a plurality of characters as the RT data. Thus, the data of a plurality of groups are necessary in order to broadcast the RT data having one meaning. If the presently broadcasted program is a music program, the information indicated by the RT data may be the title thereof. If the presently broadcasted program is a sport program such as a baseball broadcast, it may be results of games on other stadiums.
By displaying the above explained RT data, the user can obtain various information related to the broadcasted program.
However, since the RDS broadcast receiver is constructed such that the received RT data are displayed in the order of reception, there is a problem that, even if the user wishes to watch the RT data prior to the RT data multiplexed on the presently received broadcast wave, it cannot be displayed.
Namely, after the once received RT data are displayed, the nextly received RT data are decoded and displayed, so that the previously displayed content of the RT data cannot be displayed again.
Thus, it may be proposed to print out the received RT data one after another. However in this case, the size of the apparatus becomes large and is not suitable anymore as a small receiver such as an on-vehicle type.